Make iOS more responsive

[guusdk]

As explained in https://github.com/anurodhp/Monal/issues/354#issuecomment-614562560:
If a stream management ack is not received for a certain time (in prosody I use 30 seconds as default), send pushes for all messages in the smacks queue (but only once!) and directly trigger pushes for all messages coming after this until an ack is finally received or the session gets hibernated.

If you don't do this, depending on the TCP timeout (up to 8 minutes) the conversation will be disrupted for that long (or even longer if you don't handle pushes for stanzas still in the queue when a session gets hibernated).